The invention relates to an image projector of the generic type defined in the preamble to claim 1.
Known CRT image projectors, which operate in raster and calligraphic modes (U.S. Pat. No. 4,614,941), and are generally referred to as raster-calligraphic projectors, are used in, for example, flight simulators for displaying a computer-generated image of the aircraft environment. In raster mode, in which the image is written by horizontal and vertical deflections of the light beam, as in a television image, the actual environment scenario is represented with all of the details, such as the tower, landing strip, houses, roads, trees and the like; the calligraphic mode, in which the light or electron beam can be moved in any direction and at any speed, from non-movement to a high-speed pivot, permits the simultaneous display of the very bright runway lighting and colored regions within the environment scenario, resulting in extremely realistic displays of the airfield and its surroundings, as well as the surrounding landscape.
The light flux of raster-calligraphic CRT projectors is limited by the cathode-ray tube (CRT), and cannot increase significantly, so the image projection for representing a sufficiently bright simulated image is performed in darkened rooms. In raster-calligraphic CRT projectors, the raster component and the calligraphic component of the total image are written one after the other. This limits the image-repetition rate of the projector. If a large number of calligraphically-displayed lights (runway lighting) is displayed, or the image resolution is very high, the raster component must be displayed in an interlaced manner, in which case the lights are represented calligraphically between the two half-images. The use of half-images leads to flickering of the total image.
Laser projectors possessing a considerably higher light flux are used for projecting significantly brighter images that also have adequate contrast and brightness under daylight conditions. Currently, however, these laser projectors can only be operated strictly as raster projectors.
It is the object of the invention to render a raster-calligraphic image projector of the type mentioned at the
The light flux of raster-calligraphic CRT projectors is limited by the cathode-ray tube (CRT), and cannot increase significantly, so the image projection for representing a sufficiently bright simulated image is performed in darkened rooms. In raster-calligraphic CRT projectors, the raster component and the calligraphic component of the total image are written one after the other. This limits the image-repetition rate of the projector. If a large number of calligraphically-displayed lights (runway lighting) is displayed, or the image resolution is very high, the raster component must be displayed in an interlaced manner, in which case the lights are represented calligraphically between the two half-images. The use of half-images leads to flickering of the total image.
In a known image projector of the type mentioned at the outset (U.S. Pat. No. 5,582,518), the partial beam that writes the raster component is generated by a CRT, and the partial beam that writes the calligraphic component is generated by a laser. After the two partial beams have been modulated and deflected appropriately, they are guided by a semi-transparent mirror to a fish-eye lens that images the two separate images together on a spherical projection display. In a modified embodiment of this image projector, the CRT is replaced by a second laser, and the two image components of the projected image are written in the calligraphic mode.
In a known arrangement for generating polarized light (U.S. Pat. No. 5,073,830), a non-polarized light beam that is emitted by a light source, e.g., an HeNe laser, is split by a polarization beam splitter into two polarized partial beams having a half-brightness, and whose polarization planes are rotated by 90xc2x0 relative to one another. The one partial light beam is guided directly to a lens, and the other partial beam is guided to the lens via a 90xc2x0 deflection mirror and a xcex/2 plate; the lens focuses them onto a common spot. The light source that is formed in this way and radiates polarized light is used for, for example, a video projector having a xe2x80x9cliquid-crystalxe2x80x9d display.
In a known image projector (WO 99/12358), after the laser beams emitted by the three lasers for the colors red, green and blue are modulated, they are guided with the image content by a light waveguide to a deflection system that images the laser beams on a display.
It is the object of the invention to render a raster-calligraphic image projector of the type mentioned at the outset laser-capable, so raster-calligraphically-written images can be projected with a much greater brightness.
The object is accomplished by the features of claim 1.
An advantage of the raster-calligraphic image projector in accordance with the invention is that it uses a laser beam as the projection beam, and therefore has a much higher available light flux. Unlike in calligraphic CRT projectors, the splitting of the laser beam into two partial beams allows the raster component and the calligraphic component to be projected simultaneously, so the image-repetition in the raster component is not affected by the number of calligraphically-represented lights. Therefore, high-resolution images having numerous pixels and, simultaneously, a large number of light points, are also projected xe2x80x9cnon-interlaced.xe2x80x9d The light points in the calligraphic component can be represented with a far sharper contrast. Their contrast to the raster component results from the longer sojourn of the partial laser beam at the light points relative to the sojourn of the other partial laser beam at a pixel of the raster line. In the use of a beam splitter that splits the two partial beams in a 1:1 ratio, with 1000 pixels per line in the raster component and five light points to be displayed in the calligraphic component, the partial laser beam for the light point remains 1000:5=200 times as long at one position. The maximum contrast for one light point is 200:1. In the display of numerous light points in the calligraphic component, a different splitting ratio can be selected for splitting the laser beam, so the high light flux compensates the shorter sojourn of the partial laser beam at the individual light points. Guiding together the separately-modulated partial beams of different polarities permits a virtually loss-free superposing of the two partial beams in the projection head.
Advantageous embodiments of the image projector in accordance with the invention, and advantageous modifications and embodiments of the invention, ensue from the further claims.
In accordance with an advantageous embodiment of the invention, the polarization directions of the polarized partial beams are rotated 90xc2x0 relative to one another. The use of differently-polarized partial beams in accordance with the invention permits the virtually loss-free superposing of the two partial beams in the projection head. calligraphic component, the partial beam for the light point remains 1000:5=200 times as long at one position. The maximum contrast for one light point is 200:1. In the display of numerous light points in the calligraphic component, a different splitting ratio can be selected for splitting the laser beam, so the high light flux compensates the shorter sojourn of the partial laser beam at the individual light points.
Advantageous embodiments of the image projector in accordance with the invention, and advantageous modifications and embodiments of the invention, ensue from the further claims.
In accordance with an advantageous embodiment of the invention, the polarization directions of the polarized partial beams are rotated 90xc2x0 relative to one another. The use of differently-polarized partial beams in accordance with the invention permits the virtually loss-free superposing of the two partial beams in the projection head.
In accordance with a preferred embodiment of the invention, a xcex/2 plate is positioned in the beam path of one of the two partial beams for rotating the polarization directions.
In accordance with a preferred embodiment of the invention, a xcex/2 plate is positioned in the beam path of one of the two partial beams for rotating the polarization directions.
In accordance with a preferred embodiment of the invention, the modulated partial beams are coupled into glass fibers that maintain the beam polarization, and are supplied to a projection head by being coupled back out of the glass fibers, and optically superposed for projection onto a display. This division of the image projector into a laser component and a modulation component, on the one hand, and a projection component, on the other hand, permits a spatial separation of the two components, which is advantageous in an application in a flight simulator, because only the lower-weight projection head must be disposed on the mobile part of the simulator; the weight of the mobile part can therefore be kept low.